1. Field of the Invention
The present invention relates to a method of producing a transparent conductive film for use with a liquid crystal display.
2. Description of the Prior Art
Liquid crystal displays which are widely used as display units of portable calculators or watches, television receivers, and visual display terminals of OA devices, have been improved in performance and increased in screen size.
Such a liquid crystal display has a transparent conductive film thereof which serves as an electrode and is substantially produced by coating a planar, polished glass substrate with a layer of silicon dioxide (SiO.sub.2) for preventing penetration of alkali ions, forming on the silicon dioxide layer by sputtering a transparent conductive thin film of a ceramic material consisted mainly of indium tin oxide (ITO)-a mixture of indium oxide and tin oxide, and etching the ITO thin film by a photolithograph patterning technique.
As a further enlargement of a display panel and operation with high-speed response are now desired, such a transparent conductive film is intended to be low in resistance. However, the ITO thin film produced by a known sputtering technique exhibits as high as 1.times.10.sup.-4 .OMEGA..multidot.cm of resistivity, failing to satisfy the foregoing requirement. For improvement, a transparent conductive film accompanied with auxiliary metal lines has been proposed which is produced by arranging a pattern of auxiliary metal lines, a dozen or more of micrometers in line width, of e.g. a nickelchrome alloy over a transparent film.
In the prior art, a desired pattern of auxiliary metal lines is developed by forming a thin film of a nickel-chrome or gold-chrome alloy on a transparent conductive film, forming a photoresist pattern by a photolithograph technique on the thin film, and etching the thin film of nickel-chrome or gold-chrome alloy by chemically removing the unwanted portions. The prior art method however requires a considerable number of procedures including vacuum deposition, photolithograph processing, etching, and removal of photoresist materials. Also, a surplus of metal film regions are formed during the vacuum deposition thus increasing the cost of production.
Also, a screen printing technique is employed for forming a line pattern of metal resinate (a type of ink made from a metallorganic material), in which the pattern can cover a considerable area and the cost of production can be reduced. However, the pattern of lines is hardly developed at an accuracy of less than several tens of micrometers in the width of each line. Accordingly, no improvement has been attempted on the methods of forming supplementary metal lines on an ITO layer with the use of a known printing technique.